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FXUS66 KHNX 082220 AFDHNX

Area Forecast Discussion National Weather Service Hanford CA 220 PM PST Fri Dec 8 2023


SYNOPSIS
A cooling trend will continue over the forecast region into the weekend as northwesterly flow sets up aloft. Stronger winds are projected to continue in the Mojave Desert Slopes this morning with reasonable confidence of recurrence in the Southern Kern County mountains on Saturday with the development of Santa Ana winds. Freezing temperatures are possible across the rural areas of the San Joaquin Valley late Friday night and each subsequent night through next Wednesday.

KEY MESSAGES

1) Freeze Warning is in effect for rural areas of the San Joaquin Valley from 2 AM PST Saturday until 8 AM PST Wednesday

2) Breezy conditions will occur in the Southern Kern County Mountains on Saturday

DISCUSSION
The minor shortwave disturbance that brought a few showers over the northern portion of the San Joaquin Valley this week is just east of the region. Water Vapor imagery illustrates the incoming ridge that will cause subsidence and drier conditions just off the California coast. Due to the tightened surface gradient increasing winds and cyclonic flow behind the departing shortwave, a west to northwesterly wind flow has set up. The aforementioned flow and rise in winds created an upsloping fog event along in the Kern and Tulare county foothills. The influence of a southwesterly low level jet allowed the fog and low clouds to spread into the San Joaquin Valley. Visible satellite depicts low level clouds Fresno south to Bakersfield. These clouds should clear from north to south as the low level jet wanes and the northwest steering flow pushes the clouds out of the area.

In addition to the winds, the aforementioned departing trough has ushered in cooler temperatures with a cold northwesterly flow.
Near normal temperatures are in the cards today and Saturday for Central California. However, overnight lows will cascade to near freezing and sub-freezing, especially in the rural areas of the San Joaquin Valley. This has led to the upgrade of a Freeze Watch to a Freeze Warning in effect from late Friday night until Wednesday morning. The following are chances from probabilistic guidance for sub-freezing morning temperatures for select areas of the San Joaquin Valley on Saturday:

Delano 79% Visalia 69% Hanford 64% Merced 64% Porterville 59% Reedley 34% Fresno 4%

Wind speeds associated with the tightened gradient from the shortwave system have begun to relax over the Mojave Desert Slopes this afternoon. Calmer winds are expected to remain overnight but due to the interaction between the incoming, building ridge, and departing low, in addition to the increased Santa Ana wind event, several short-range deterministic models and ensembles support elevated winds on Saturday. HRRR Probabilities for greater than 25mph over much of the southern Kern County mountains portrays a 50-80% chance of occurrence, with isolated areas reaching 30mph. Winds will subside in the evening as the ridge fully entrenches itself over the west coast. The ridge will allow for above normal temperatures to occur on Sunday and Monday; 5 degrees above normal with highs in the SJV and desert expected to be in the low to mid-60s.

Cluster analysis and medium range deterministic model solutions are trending toward a shortwave trough in the Pacific NW breaking down the ridge on Monday allowing for zonal flow to set up aloft early next week, before a weak ridge builds back in Wednesday slightly increasing temperatures. Probabilistic guidance suggests a 30-60% chance for maximum afternoon temperatures to exceed 65 degrees in the San Joaquin Valley Wednesday and Thursday.

AVIATION
MVFR conditions in areas of mist/haze possible beginning at 09Z Saturday. Otherwise, VFR conditions will prevail across Central California over the next 24 hours.

AIR QUALITY ISSUES
On Friday December 8, 2023, Fireplace/Wood Stove Burning Status is: No burning unless registered in Fresno and Kern Counties.
Burning Discouraged in Kings,Madera, Merced, and Tulare Counties, and Kern (Greater Frazier Park Area) and Sequoia National Park and Forest.

CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low
medium
and high. Please visit www.weather.gov/hnx/certainty.html for additional information and/or to provide feedback.



HNX WATCHES/WARNINGS/ADVISORIES
Freeze Warning from 2 AM Saturday to 8 AM PST Wednesday for CAZ301>303-305-306-309>312-315.

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